Until a few years ago, most commercial canners practiced batch-wise cooking of canned foods.
Then conveyor-fed continuous cookers were developed and marketed, principally by FMC Corporation.
A typical continuous cooker accepts one continuous row of filled and sealed but unlabeled cans, rolls the cans on their sides in a helix extending from end to end on the cylindrical inner surface of a drum while applying heat to the cans, e.g. using high-pressure steam.
The cans which have passed through the cooker are then typically cooled, palleted and warehoused. When the canner receives an order to ship, the palleted cans are withdrawn from storage, labeled with the desired labeling, boxed and shipped.
Generally, a continuous cooker is configured to process one uniform size of can, for instance 303 .times. 404, one pound cans and substantial modifications are needed to switch can size. However, these continuous cookers are able to cook canned food quite rapidly, so rapidly in fact that generally two or more can filling and closing lines must serve one continuous cooker if the continuous cooker is to be run near full capacity.
As a typical example, many filling and closing lines processing one pound food cans operate at an output rate of about 200 to 250 cans per minute, whereas a typical continuous cooker has an operating capacity of 600 1 pound cans per minute. Thus, either such a continuous cooker must be fed by 2 or 3 can filling and closing lines, or run with a full volume of steam wastefully cooking only a few cans and a lot of empty space, or run in a batch-wise manner.
The economics of commercial canning is such that both running a continuous cooker part full or as a batch-wise cooker is a losing proposition for both money and energy.
For the typical large volume canner and for the typical small volume canner, the problem just outlined is unlikely to arise.
The large volume canner can expect to be packing so much of one sort of food that it is feasible to feed their continuous cooker using two, three or several filling and closing lines each putting the same kind and grade of food in the same cans.
The small volume canner lacks the expectation of being able to fully use a continuous cooker. Thus, such a unit is generally not part of a small canner's equippage.
The problem of using a continuous cooker efficiently and profitably is most likely to arise for a medium volume canner. Such a canner may have operational peaks during which a continuous canner can be served by a plurality of filling and closing lines all processing the same kind and quality of food. However, at other times the volume or anticipated length of run may be insufficient to warrent operating more than one filling and sealing line to process a particular kind and quality of food.
Faced with that potential, some medium-sized canners have acquired continuous cookers, used them efficiently at times and inefficiently at other times and have hoped increasing business volume would improve their efficiency. Other medium-sized canners have simply put off acquiring continuous cookers, despite their obvious advantages.
While a medium-sized canner may not have the volume of one kind and quality of food to run several filling and sealing lines at once to can that food, it is likely to have sufficient business volume to be running two or more filling and sealing lines at once, each processing a different kind and/or quality of food. For instance, one line might be packing Grade A peas and another might be packing Grade B peas, or one might be packing cream-style corn while the other is packing whole-kernel corn.
Prior to the present invention, others have made some efforts to find an acceptable way to serve a continuous cooker with the randomly mixed output of a plurality of filling and sealing lines that are processing foods of a different kind or quality. Basically, these efforts have centered about marking the cans from each line in an optically sensible manner. These are examples of what has been tried: brass-colored lids on one line's cans and silver-colored lids on the other line's cans; spots of highly reflective paint applied to the cans of one line, but not to those of the other; and different product codes embossed on the can lids. Sensing devices have ranged from simple brightness detectors through complex optical character readers.
However, all these optical techniques have a common problem: at the point in the process where the mixed cans are to be separated, the cans most often are covered with beads of moisture, because they have just gone through a cooling spray and/or because they have cooled below the dew point of their environment and condensation has occurred thereon. Simply put, the moisture beads reflect light in a sufficiently unpredictable manner as to introduce an unacceptable level of uncertainty in a discrimination based on optical cues.
These prior art systems have other undesirable features. Odd-colored lids are unacceptable to some of the canners' customers and to some ultimate consumers. Their use requires the canners to stock two or more colors of lids and to avoid mistakes in supplying the right color of lids to each canning line. Applied spots of paint or the like require spot applying machinery which can become fouled or exhausted of paint resulting in a number of identically-appearing intentionally spotless and unintentionally spotless cans becoming mixed, then unsortable. In addition, processing in a cooker can remove some paint spots applied under less-than-optimum conditions such as improper composition, mixing or drying of the paint.